The present invention is directed to centrifuge rotors having swinging fluid sample containers or tubes and, more specifically, is directed to a rotor which utilizes a liquid support medium within the rotor to provide buoyant support to the swinging containers or tubes when the rotor is operating at very high speeds.
Various configurations of rotors utilizing swinging buckets or other types of containers are presently used in centrifuges. Typically, fluid samples are placed within centrifuge tubes which are supported within some type of container or bucket that is mounted on a metal support in the rotor. The container is mounted in such a way that it will pivot through an arc of approximately 90.degree. between its position at rest and its position during operational speeds of the rotor. When the centrifuge tube is at rest, its longitudinal axis generally aligns itself in a somewhat parallel position with respect to the spin axis of the rotor. However, during high speed centrifugation, the swinging tube moves radially outward in response to centrifugally induced forces on the tube, so that the longitudinal axis of the tube is approximately perpendicular to the spin axis of the rotor.
It is important in centrifugation that motion of the fluid sample in the tube during rotor acceleration and deceleration is minimized. Interaction between particles and the tube wall should be minimized and the sedimentation of flotation particles should take place generally along the longitudinal axis of the tube. It has been found that a swinging tube type of centrifuge rotor has these desirable features and, therefore, is utilized in many centrifugation experiments as being the only successful or practical approach. This is true with respect to the example of the centrifugal separation of liquid protein components of human serum for scanning by light scattering.
One of the major concerns with respect to utilization of swinging tube type rotors is the fact that tremendous forces of thousands of kilograms are exerted not only on the tube, but also on the supporting heads and pivot junctions that are utilized in the pivoting design of the tube or the container holding the tube. During ultracentrifugation some rotors reach operational speeds of 150,000 rpm to 200,000 rpm. Therefore, the tube and overall supporting mechanism for the tube must be made of a very high strength material. In addition, the pivot junction is usually significantly large and is designed with great care.